1. Field of Invention
The invention relates to a communication device and a communication method. In particular, the invention relates to an asymmetric gain communication device whose receiving antennas have larger gains than the transmission antenna and whose receiving antennas are selected to use according to the communication quality. The invention also pertains to the communication thereof.
2. Related Art
In recent years, the popularity and rapid developments of wireless communications have boosted the invention of various kinds of wireless communication devices. Different countries have different regulations on the emission power of specific frequencies in order to effectively use and control the wireless spectrum. Therefore, different wireless communication protocols are used worldwide. However, this limits the signal transmission distance.
Generally speaking, a wireless communication device has one antenna for transceiving signals. Its emission power is regulated by local laws. This means that if one wants to increase the signal transmission distance by increasing the antenna gain, the emission power of the gain has to be raised beyond the requirements of local laws. Under the constraints of regulations, vendors have been trying hard to increase the signal transmission distances of wireless communication devices.
In view of this, some vendors propose to increase the antenna gain and detect whether the emission power exceeds the regulations. If the emission power is too high, then it automatically reduces the power before further signal emissions. Otherwise, the power remains the same. However, increasing the antenna gain will result in a narrow radiation angle for the antenna. It is then easily affected by the environment to have deviations and communication instability.
In summary, the prior art long has the problem of being unable to extend signal transmission distances under the constraints of emission power regulations. It is therefore imperative to provide a better solution.